Fluid sensors are known which utilize the drag forces exerted on a body by the flowing fluid to determine the velocity of the latter. Drag forces arise in a direction parallel to the flow of fluid and result from the resistance presented by the body to the fluid flow. However, body forms that give rise to drag forces of a magnitude that can be used to provide an appropriate output from the sensor often also give rise to turbulence in the fluid flow. This causes non-linearities or other discontinuities and anomalies to appear in the output of the sensor, adversely affecting its accuracy unless compensation is provided for same, and rendering the instrument hard to use. Such a sensor may also cause a significant pressure drop in the flowing fluid. Such a pressure drop may adversely affect the operation of apparatus associated with the fluid sensor or the application to which the fluid sensor may be put. For example, when such a sensor is used to measure the breathing gas flows of a patient, it may increase the exertions required of the patient in breathing.